Method of removing hydrogen sulfide

ABSTRACT

The invention provides a method of removing hydrogen sulfide from hydrocarbon fluids. The method involves using a nitroxide molecule to promote a sulfide scavenger such as alkyl-triazine. The nitroxide effectively accelerates the scavenger&#39;s activity. This allows for the avoidance of the introduction of halides into the hydrocarbon stream.

CROSS-REFERENCE TO RELATED APPLICATIONS

None.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

BACKGROUND OF THE INVENTION

This invention relates generally to the treatment of sour gas and liquid hydrocarbon to remove or reduce the levels of hydrogen sulfide therein. The toxicity of hydrogen sulfide in hydrocarbon streams is well known in the industry and considerable expense and efforts are expended annually to reduce its content to a safe level.

In large production facilities, it is generally more economical to install a regenerative system for treating sour gas streams. These systems typically employ a compound used in an absorption tower to contact the produced fluids and selectively absorb the hydrogen sulfide and possibly other toxic materials such as carbon dioxide and mercaptans. The absorption compound is then regenerated and reused in the system. Typical hydrogen sulfide absorption materials include alkanolamines, PEG, hindered amines, and other species that can be regenerated.

Nonregenerative scavengers for small plant hydrogen sulfide removal fall into four general categories: 1) aldehyde based, 2) metallic oxide based, 3) caustic based, and 4) other processes. In the removal of hydrogen sulfide by nonregenerative compounds, the scavenger reacts with the hydrogen sulfide to form a nontoxic compound or a compound, which can be removed from the hydrocarbon. For example, when formaldehyde reacts with hydrogen sulfide, a chemical compound known as formthionals (e.g., trithiane) is formed.

Prior Art aldehyde scavengers typically include low molecular weight aldehydes and ketones and adducts thereof. The low molecular weight aldehydes may also be combined with an alkyl or alkanolamine as disclosed in U.S. Pat. No. 4,748,011. Other aldehyde derived scavengers include the reaction product of low molecular weight alkanolamines and aldehydes as disclosed in U.S. Pat. No. 4,978,512. PCT Application WO 92/01481 discloses a method of reducing sulfides in a sewage gas using certain tri-substituted-hexahydro-s-triazines. German reference DE4027300 discloses a regenerative solvent for removing H₂S and mercaptans. U.S. Pat. No. 5,347,004 discloses the use of 1,3,5 alkoxyalkylene hexahydro triazines. PCT Application WO 91 US 5232 discloses hydroxyalkyl triazine scavengers, specifically an N,N′,N″-tris(2-hydroxyethyl)hexahydro-s-triazine. U.S. Pat. No. 5,774,024 discloses the combination of an alkyl triazine scavenger and quaternary ammonium salt, where the quaternary ammonium salt enhances the effectiveness of the alkyl-triazine.

Thus there is clear need and utility for an improved method of scavenging hydrogen sulfide from hydrocarbon fluids. The art described in this section is not intended to constitute an admission that any patent, publication or other information referred to herein is “prior art” with respect to this invention, unless specifically designated as such. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 CFR §1.56(a) exists.

BRIEF SUMMARY OF THE INVENTION

At least one embodiment of the invention is directed towards a method for removing hydrogen sulfide from a hydrocarbon fluid. The method comprises contacting the fluid with an effective amount of sulfide scavenger formulated with a nitroxide promoter. The amount of nitroxide promoter is sufficient to accelerate the scavenging action of the scavenger in comparison to the scavenging action of the scavenger in the absence of the nitroxide promoter.

DETAILED DESCRIPTION OF THE INVENTION

For purposes of this application the definition of these terms is as follows:

“Alkyl-triazine” means a molecule according to the formula:

Where R₁, R₂, R₃ are Alkyl groups such as methyl, ethyl, propyl, isopropyl, t-butyl, etc. or are substituted alkyl groups such as CH₂CH₂OH, and R₁, R₂, R₃ can all be the same group or one or more different groups. Alkyl-triazines include but are not limited to the triazines disclosed in U.S. Pat. No. 5,744,024.

“Hydrocarbon fluid” means a liquid or gas predominantly comprising organic material including but not limited to kerosene, crude oil, distillate fuels, fuel oil, heating oils, diesel fuel, gasoline, jet fuel, bunker fuel oils, and any combination thereof.

“Methyltriazine” means an alkyl-triazine in which R₁, R₂, and R₃ are all methyl groups.

“Nitroxide” means a composition of matter according to the formula:

where R₁ R₂ and R₃ are any alkyl group containing 1-30 carbon atoms and includes cyclic compounds. “Non-Regenerative Scavenger” means a scavenger, which is consumed by the process of scavenging.

“Regenerative Scavenger” means a scavenger, which is not consumed by the process of scavenging.

“Promoter” means a composition of matter that in and of itself does not scavenge, but when combined with a known scavenger, significantly increases the effectiveness of the scavenger.

“Salt” means a compound comprising an anion and a cation which usually ionizes in solution.

“Scavenger” means a composition of matter, such as but not limited to alkyl triazines, useful in reducing the amount of some other composition of matter, such as but not limited to hydrogen sulfide, in a fluid medium.

In the event that the above definitions or a description stated elsewhere in this application is inconsistent with a meaning (explicit or implicit) which is commonly used, in a dictionary, or stated in a source incorporated by reference into this application, the application and the claim terms in particular are understood to be construed according to the definition or description in this application, and not according to the common definition, dictionary definition, or the definition that was incorporated by reference. In light of the above, in the event that a term can only be understood if it is construed by a dictionary, if the term is defined by the Kirk-Othmer Encyclopedia of Chemical Technology, 5th Edition, (2005), (Published by Wiley, John & Sons, Inc.) this definition shall control how the term is to be defined in the claims.

In at least one embodiment, the amount of hydrogen sulfide in a hydrocarbon fluid is reduced by the introduction of an alkyl-triazine scavenger with a nitroxide promoter. The promoter increases the effectiveness of the alkyl-triazine scavenger. Nitroxide is superior to the prior art quarternay ammonium salt promoters because nitroxide is a single component and does not contain halides such as chloride.

The effectiveness of a nitroxide as a promoter is unexpected because it is a single neutral compound. In at least one embodiment the promoter is from 1-25% of the scavenger-promoter containing composition.

In at least one embodiment, at least a portion of the triazines are synthesized according to the process described in U.S. Pat. No. 5,744,024.

In at least one embodiment the ntiroxide is mixed with a solution of alkyl triazine where the solvent can be water and the nitroxide bearing solution is introduced into the hydrocarbon fluid. In at least one embodiment the nitroxide introduction is simultaneous to the alkyl-triazine introduction. The properties of the ntiroxide promoter are such that it is highly effective in a number of different hydrocarbon fluids.

One advantage of the use of the nitroxide promoter with a scavenger over the prior art scavengers is that the nitroxide promoter is not a salt (it is not a combination of an anion and a cation) and therefore lacks halides and in particular lacks chloride.

In at least one embodiment a scavenging formulation is used in a hydrocarbon stream. The formulation comprises a solvent, alkyl-triazine, and nitroxide. The solvent is selected from the list consisting of water, alcohol, aromatic solvent, a solvent that mutually solvates alkyl-triazine, and nitroxide and any combination thereof. The formulation can be introduced into the hydrocarbon stream by mechanical means including but not limited to injection pumps or any mechanism disclosed in U.S. Pat. Nos. 5,744,024 and 5,840,177. In the context of gaseous hydrocarbon fluids, the gas may be passed through an absorption tower containing a scavenging formulation.

In at least one embodiment the hydrocarbon fluid is in a liquid state. In at least one embodiment the hydrocarbon fluid is in a gaseous state.

EXAMPLES

The foregoing may be better understood by reference to the following example, which is presented for purposes of illustration and is not intended to limit the scope of the invention.

Samples of sour hydrocarbon streams (fuel oils) were tested to determine the efficiency of the triazine formulated with promoter versus the triazine formulated without a promoter. The samples were comparatively treated with various dosages of methyltriazine scavenger, methyltriazine scavenger with a promoter, and the amounts of residual H₂S for the various samples were recorded. Table 1 compares the inventive composition at different concentrations, Table 2 compares promoted scavenger with non-promoted scavenger, and table 3 compares methyltriazine with and without promoter over time.

TABLE 1 Comparison of promoter at 3 different concentrations in vacuum gas oil for 2 hours at 60° C. Dose H2S Percent Dose Sample # Treatment (ppm) (ppm) Reduction Ratio Untreated 0 200 0 1 Methyltriazine + 60 100 50 0.3 2.5% nitroxide 2 Methyltriazine + 60 120 40 0.3 5% nitroxide 3 Methyltriazine + 60 130 35 0.3 10% nitroxide

TABLE 2 Comparison of promoted and non-promoted triazine, in kerosene for 2 hours Dose H2S Percent Dose Sample # Treatment (ppm) (ppm) Reduction Ratio Untreated 0 1300 1 Methyltriazine + 260 70 95 0.2 5% Quaternary ammonium 2 Methyltriazine + 260 90 93 0.2 5% nitroxide 3 Methyltriazine 260 120 91 0.2 Untreated 0 950 1 Methyltriazine + 284 30 97 0.3 5% Quaternary ammonium 2 Methyltriazine + 284 70 93 0.3 5% nitroxide 3 Methyltriazine 284 80 92 0.3

TABLE 3 Comparison of alkyl-triazine with and without promoter over time in kerosene Sample Dose H2S Percent Dose Time # Treatment (ppm) (ppm) Reduction Ratio (min) Un- 0 1200 0 0 treated 1 Methyltriazine + 400 300 75 0.3 15 nitroxide 2 Methyltriazine + 400 200 83 0.3 30 nitroxide 3 Methyltriazine + 400 85 93 0.3 60 nitroxide 4 Methyltriazine + 400 75 94 0.3 90 nitroxide 5 Methyltriazine + 400 75 94 0.3 120 nitroxide Un- 0 600 0.3 0 treated 1 Methyltriazine 200 250 58 0.3 15 2 Methyltriazine 200 230 62 0.3 30 3 Methyltriazine 200 110 82 0.3 60 4 Methyltriazine 200 60 90 0.3 90 5 Methyltriazine 200 70 88 0.3 120

The vapor space hydrogen sulfide levels were measured according to the procedure described by ASTM D5705-03. The test procedure was modified for tables 2 and 3 by performing the test in kerosene at room temperature, which was approximately 22° C. instead of 60° C.

This data demonstrates that the presence of the nitroxide enables the methyltraizine scavenger to reduce the levels of H₂S faster than methyltriazine does without the promoter.

While this invention may be embodied in many different forms, there are shown in the drawings and described in detail herein specific preferred embodiments of the invention. The present disclosure is an exemplification of the principles of the invention and is not intended to limit the invention to the particular embodiments illustrated. All patents, patent applications, scientific papers, and any other referenced materials mentioned herein are incorporated by reference in their entirety. Furthermore, the invention encompasses any possible combination of some or all of the various embodiments described herein and incorporated herein.

The above disclosure is intended to be illustrative and not exhaustive. This description will suggest many variations and alternatives to one of ordinary skill in this art. All these alternatives and variations are intended to be included within the scope of the claims where the term “comprising” means “including, but not limited to”. Those familiar with the art may recognize other equivalents to the specific embodiments described herein which equivalents are also intended to be encompassed by the claims.

All ranges and parameters disclosed herein are understood to encompass any and all subranges subsumed therein, and every number between the endpoints. For example, a stated range of “1 to 10” should be considered to include any and all subranges between (and inclusive of) the minimum value of 1 and the maximum value of 10; that is, all subranges beginning with a minimum value of 1 or more, (e.g. 1 to 6.1), and ending with a maximum value of 10 or less, (e.g. 2.3 to 9.4, 3 to 8, 4 to 7), and finally to each number 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10 contained within the range.

This completes the description of the preferred and alternate embodiments of the invention. Those skilled in the art may recognize other equivalents to the specific embodiment described herein which equivalents are intended to be encompassed by the claims attached hereto. 

1. A method of reducing the amount of hydrogen sulfide in a hydrocarbon fluid comprising contacting the fluid with an effective amount of a composition, the composition comprising a sulfide scavenger and a nitroxide promoter wherein the amount of nitroxide promoter is sufficient to accelerate the scavenging action of the scavenger in comparison to the scavenging action of the scavenger in the absence of the nitroxide promoter.
 2. The method of claim 1 wherein the scavenger is an alkyl-triazine.
 3. The method of claim 1 wherein the hydrocarbon fluid is liquid.
 4. The method of claim 1 wherein the method results in no halides being added to the hydrocarbon fluid. 